Of the roughly 40 million Americans suffering from hearing loss, 10 million can be attributed to noise-induced hearing loss (NIHL). NIHL can be caused by a one-time exposure to loud sound as well as by repeated exposure to sounds at various loudness levels over an extended period. Damage happens to the microscopic cells found inside the cochlea part of the inner-ear. These cells respond to mechanical sound vibrations by sending an electrical signal to the auditory nerve. The healthy human ear can hear frequencies ranging from 20Hz to 20,000 Hz, and different groups of these cells are responsible for different frequencies (rate of vibrations). Over time, the cell’s hair-like stereocilia may get damaged or broken and if enough of them are damaged, hearing loss results. The high frequency area of the cochlea is often damaged by loud sound.

How is Sound measured?

The energy in a sound wave is measured in Decibels (dB). Like a temperature scale, the decibel scale goes below zero. The average person can hear sounds down to about 0 dB, the level of rustling leaves. Some people with very good hearing can hear sounds down to -15 dB. But if sound reaches beyond 85 dB it can cause permanent damage to your hearing. The longer you listen to a sound at high dB will affects how much damage it may cause. Low range sounds may be listened to safely, they will cause damage even over extended periods, but exposure to even some common sounds may cause permanent damage. And extended exposure to sounds above 85 dB can cause permanent damage to the cells in your inner ear, leading to hearing loss.

An idlingdiesel engine is loud enough at 85 dB to cause permanent damage after only 1 workday (8 hours).

When listening to a personal music system with stock earphones at a maximum volume, the sound generated can reach a level well over 100 dBA, loud enough to begin causing permanent damage after just 15 minutes per day!

Decibel Exposure Time Guidelines

Recent studies suggested that nearly 50 percent of teens and young adults get exposed to unsafe volume levels from mobile devices. And 40% of that is potentially damaging levels of sound. That’s over 1 billion people at risk, which is why setting a volume limit is probably a good idea.

Some studies have found that people in their 20s have hearing loss more typical of people aged 50 years and older because of exposure to music at this volume.

For every 3 dB over 85dB, the permissible exposure time before possible damage can occur is cut in half. - Recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and the CDC, 2002.

Audio devices and mobile phones including iPhone have a sound level of 100 dB or louder. iPhones can produce a maximum of 115 decibels (software limits European iPods to 100 dB; U.S. models have been measured higher), the equivalent of attending a rock concert amplification.

– Does loudness vary a great deal from one brand/model to another?

The output levels across various brands of models tested are about the same, especially in the high decibel output. Apple’s iPhone iOS and the latest versions of Android OS have a ‘safe volume’ warning built into their software.

– What about the headset, over the ear vs. ear buds; is one less damaging than the other?

It can depend on how loud you set the volume and for how long you listen to that volume. Despite their inclusion with every mobile phone, researchers stress caution when using earbuds.

Because of their ‘in-ear’ design, earbuds are more likely to cause hearing damage than headphones that sit on or over the ear. They can also be up to 9 dB louder than over-the-ear headphones. This isn't a big deal when going from 40 to 50 dB, but more serious when going from 70 to 80.

– How loud is too loud when the volume control doesn’t provide information on the output level?

A rule of thumb is if you cannot understand someone talking to you in a normal speaking voice when they are an arm’s length away… it’s probably too loud. This rule works with standard earbuds and headphone.

– Is there a rule of thumb about setting limits on the volume wheel?

Since the combination of volume and length of listening can cause hearing loss, researchers recommend applying the 60/60 rule. This rule suggests listening to an iPhone for 60 minutes at 60 percent of its maximum volume, then taking a break. Ears that get a rest have time to recover and are less likely to be permanently damaged. No more than 30 minutes at the 80% volume.

– Loud music damages the nerves in the brain

Loud music on headphones has the same effect on nerves as multiple sclerosis and causes hearing loss.

Loud music played on earphones causes hearing loss by having a similar effect on nerves as multiple sclerosis, research finds. The research shows that noise levels above 110 decibels strip insulation from nerve fibers carrying signals from the ear to the brain. Loss of the protective coating, called myelin, disrupts electrical nerve signals.

The same process, this time due to an attack from the immune system, damages nerves in the brain and results in multiple sclerosis.

It is well known that loud noises can lead to hearing problems such as temporary hearing loss or tinnitus (ringing in the ears) and even permanent hearing loss. But this is the first-time scientists have been able to identify damages to nerve cells as a result of noise exposure.

"The research allows us to understand the pathway from exposure to loud noises to hearing loss. Dissecting the cellular mechanisms underlying this condition is likely to bring a very significant healthcare benefit to a wider population. The work will help prevention as well as progression into finding appropriate cures for hearing loss", said the lead researcher Dr. Martine Hamann, from the University of Leicester in the UK.

Hearing can recover

Scientists found that myelin loss, as a result of noise exposure, re-grows in time, meaning hearing can recover.

The work is part of ongoing research into the effects of loud noises on the cochlea nucleus, a brainstem region that receives sound signals from the inner ear. Based on these results, scientists may be able to develop a future treatment method.

We at V7 are working on adding volume control limitations to headsets made for the education sector. This will help limit some of the early exposure of damaging sound levels. As part of our constant effort to bring our customers high-quality products with top features for less than the competition.

The results have been published in the scientific journal Proceedings of the National Academy of Sciences.